Expandable spinal rods and methods of use

ABSTRACT

A spinal rod having first and second end members. The end members may be flexible or rigid. An expandable intermediate section is positioned between the first and second end members. The intermediate section may be axially expandable upon the introduction of a substance into a port that may be located in either of the first and second end members or the intermediate section. The intermediate section may be expandable between a first size, where the first and second end members are spaced a first distance apart, and a second enlarged size, where the first and second end members are spaced a second greater distance apart.

BACKGROUND

Spinal rods are often used in the surgical treatment of spinal disorderssuch as degenerative disc disease, disc herniations, scoliosis or othercurvature abnormalities, and fractures. Different types of surgicaltreatments are used. In some cases, spinal fusion is indicated toinhibit relative motion between vertebral bodies. In other cases,dynamic implants are used to preserve motion between vertebral bodies.For either type of surgical treatment, spinal rods may be attached tothe exterior of two or more vertebrae, whether it is at a posterior,anterior, or lateral side of the vertebrae. In other embodiments, spinalrods are attached to the vertebrae without the use of dynamic implantsor spinal fusion.

Spinal rods may provide a stable, rigid column that encourages bones tofuse after spinal-fusion surgery. Further, the rods may redirectstresses over a wider area away from a damaged or defective region.Also, a rigid rod may restore the spine to its proper alignment. In somecases, a flexible rod may be appropriate. Flexible rods may provide someadvantages over rigid rods, such as increasing loading on interbodyconstructs, decreasing stress transfer to adjacent vertebral elementswhile bone-graft healing takes place, and generally balancing strengthwith flexibility. One disadvantage with conventional rods is that theirlength, which may span several vertebrae, may require large surgicalincisions to implant the rod. Therefore, surgical procedures requiringthe installation of an elongated rod have often required invasive openprocedures that are more costly to perform, and potentially moredangerous and more painful for the patient.

SUMMARY

Illustrative embodiments disclosed herein are directed to a spinal rodthat has first and second end members. The first and second end membersmay comprise a clamping portion for coupling with a vertebral member. Indifferent embodiments, the end members may be flexible or rigid. Anexpandable intermediate section is positioned between the first andsecond end members. The intermediate section may be axially expandableupon the introduction of a substance into a port that may be located ineither of the first and second end members or the intermediate section.Further, the port may be axially or radially located on the rod. Thesubstance may be a fluid, such as a curable liquid. The intermediatesection may be expandable between a first size, where the first andsecond end members are spaced a first distance apart, and a secondenlarged size, where the first and second end members are spaced asecond greater distance apart. The intermediate section may be flexibleor rigid. The rod may be configured to span two or more vertebrae.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of first and second assemblies comprisingspinal rods attached to vertebral members according to one embodiment;

FIG. 2 is a lateral view of a spinal rod according to one embodiment;

FIG. 3 is a cross section view of a spinal rod according to oneembodiment;

FIG. 4 is a cross section view of a spinal rod according to oneembodiment;

FIG. 5 is a cross section view of a spinal rod according to oneembodiment;

FIGS. 6A and 6B are lateral views of a spinal rod in extended andcompressed states according to one embodiment;

FIGS. 7A and 7B are lateral views of a spinal rod in compressed andextended states according to one embodiment;

FIGS. 8A and 8B are lateral views of a spinal rod in compressed andextended states according to one embodiment;

FIG. 9 is a lateral view of a spinal rod according to one embodiment;

FIG. 10 is a lateral view of a spinal rod according to one embodiment;

FIGS. 11-13 illustrate a surgical implantation process for a rodaccording to one embodiment; and

FIGS. 14-15 illustrate a surgical implantation process for a rodaccording to one embodiment.

DETAILED DESCRIPTION

The various embodiments disclosed herein are directed to spinal rodsthat are characterized by at least one expandable portion. Theexpandable portion may be compressed or left unfilled duringinstallation of the rod and may be filled with an injectable substanceonce the rod is positioned within the body. Various embodiments of aspinal rod may be implemented in a spinal rod assembly of the typeindicated generally by the numeral 20 in FIG. 1. FIG. 1 shows aperspective view of first and second spinal rod assemblies 20 in whichspinal rods 10 are attached to vertebral members V1 and V2. In theexample assembly 20 shown, the rods 10 are positioned at a posteriorside of the spine, on opposite sides of the spinous processes SP. Spinalrods 10 may be attached to a spine at other locations, including lateraland anterior locations. Spinal rods 10 may also be attached at varioussections of the spine, including the base of the skull and to vertebraein the cervical, thoracic, lumbar, and sacral regions. In oneembodiment, a single rod 10 is attached to the spine. Thus, theillustration in FIG. 1 is provided merely as a representative example ofone application of a spinal rod 10.

In one embodiment as illustrated in FIG. 1, the spinal rods 10 aresecured to vertebral members V1, V2 by pedicle assemblies 12 comprisinga pedicle screw 14 and a retaining cap 16. The outer surface of spinalrod 10 is grasped, clamped, or otherwise secured between the pediclescrew 14 and retaining cap 16. Other mechanisms for securing spinal rods10 to vertebral members V1, V2 include hooks, cables, and other suchdevices. Examples of other types of retaining hardware include threadedcaps, screws, and pins. Spinal rods 10 are also attached to plates inother configurations. Thus, the exemplary assemblies 12 shown in FIG. 1are merely representative of one type of attachment mechanism.

FIG. 2 shows an isolated view of a spinal rod 10 of the type used in theexemplary assembly 20 in FIG. 1. The exemplary rod 10 includes anexpandable portion 30. A first rod end 32 is shown attached to the leftside of the expandable portion 30 in the view provided. A second rod end34 is also shown attached to the right side of the expandable portion30. The first and second rod ends 32, 34 further include a clampingportion 33 and an enlarged flange portion 35. The clamping portion 33may be sized to fit within conventional rod securing devices such asthose shown in FIG. 1 and described above. For example, the clampingportion 33 may have a diameter within a range between about 4 and 7 mm.The rod ends 32, 34 may be constructed from a variety of surgical gradematerials. These include metals such as stainless steels, cobalt-chrome,titanium, and shape memory alloys. Non-metallic rods, including polymerrods made from materials such as PEEK and UHMWPE, are also contemplated.The spinal rod 10 may have rigid or flexible rod ends 32, 34.

The expandable portion 30 is axially expandable along the longitudinalaxis A of the rod 10 as indicated by the arrows labeled X. In one ormore embodiments, the rod 10 may be expanded through the introduction ofan injectable substance that contacts the first and second rod ends 32,34, thereby causing the first and second rod ends 32, 34 to moveopposite one another. Various techniques may be used to introduce theinjectable substance into the expandable portion 30. For example, oneembodiment of a rod 10 a depicted in FIG. 3 includes a cannulated secondrod end 34 a. The duct 36 within the second rod end 34 a connects aninterior volume 38 with the exterior of the rod 10 a. The interiorvolume 38 is defined by the first and second rod ends 32 a, 34 a and anexpandable outer sheath 42. In the embodiment shown, the sheath 42connects the first and second rod ends 32 a, 34 a. In one embodiment,the sheath 42 is constructed of a flexible biomedical grade materialincluding resins, polymers, and metals. An injectable substance may flowthrough the duct 36 into the interior volume 38 of the expandableportion 30 from an end 40 of the second rod end 34 a. As the injectablesubstance fills the interior volume 38, the substance contacts surfaces45 and 49, thus forcing the second rod end 34 a to separate from thefirst rod end 32 a as indicated by the arrow labeled X. In oneembodiment, the rod 10 a comprises a self-sealing valve 42 that preventsthe injectable substance from escaping once the interior volume 38 isfilled. In one embodiment, the self-sealing valve 42 is a check valvethat is incorporated along the duct 36 to allow the injectable substanceto flow towards the interior volume 38, but not out of the duct 36.

A variety of injectable substances may be inserted into the interiorvolume to cause the expandable portion 30 to expand. In one embodiment,the injectable substance is a fluid, such as a gas or a liquid. In oneembodiment, the injectable substance is a solid, such as a powder. Inone embodiment, the injectable substance is a curable liquid thatsolidifies after a predetermined amount of time or under the influenceof an external catalyst. For instance, an injectable liquid may cureunder the influence of heat or light, including ultraviolet light. Someexamples of in situ curable liquids include epoxy, PMMA, polyurethane,and silicone.

The exemplary rod 10 a shown in FIG. 3 includes a first perforatedprotrusion 44 coupled to the first rod end 32 a and extending inwardfrom a surface 45. Similarly, the rod 10 a includes a second perforatedprotrusion 48 coupled to the second rod end 34 a and extending inwardfrom a surface 49. The first perforated protrusion 44 includes aplurality of holes 46 that allow the injectable substance to flow intoor out of the first perforated protrusion 44. Similarly, the secondperforated protrusion 48 includes a plurality of holes 50 that allow theinjectable substance to flow into or out of the second perforatedprotrusion 48. In embodiments where the injectable substance comprises acurable liquid, the first and second perforated protrusions 44, 48 mayprovide an increased amount of surface area for a curable liquid toadhere. This may provide a more secure bond between the curable liquidand the first and second rod ends 32 a, 34 a.

In one embodiment, the first and second perforated protrusions 44, 48are cylindrical. In one embodiment, the first perforated protrusion 44is larger than the second perforated protrusion 48. Thus, in the eventthe first and second rod ends 32 a, 34 a are pushed together asindicated by the arrow labeled Y, the second perforated protrusion 48may fit substantially within the first perforated protrusion 44. In thisscenario, the first perforated protrusion 44 may contact the second rodend 34 a. Alternatively, the second perforated protrusion 48 may contactthe first rod end 32 a. In either case, overcompression of the sheath 42and damage thereto may be avoided.

An alternative embodiment of a rod 10 b is depicted in FIG. 4. In thisembodiment, the first and second rod ends 32 b, 34 b are shown as solidmembers, though this is not expressly required. The exemplary sheath 52surrounding the interior volume 54 is an accordion-style bellows. In oneembodiment, the sheath 52 is reinforced with a woven or braidedstructure. In one embodiment, the sheath 52 is reinforced with coiled orconcentric wires 56. The concentric wires 56 may be comprised of abiocompatible metal such as stainless steel, titanium alloys, ornitinol. The interior volume 54 of the expandable portion 30 b may befilled through a self-sealing valve 58 that prevents an injectablesubstance from escaping once the interior volume 38 is filled.

FIG. 5 shows an alternative embodiment of a rod 10 c that is similar torod 10 a. For instance, the second perforated protrusion 48 and theholes contained thereon 50 are substantially the same on bothembodiments of the rod 10 a, 10 c. In rod 10 c, the expandable portion30 c is defined in part by a folded sheath 142 having pleats thatoverlap one another. When the expandable portion 30 c expands under theinfluence of an injected substance, the folded sheath 142 unfolds to anextended state, such as that shown in FIG. 1.

The first rod end 32 c has a plurality of anchors 60 comprising a stemportion 62 and an enlarged head portion 64. In embodiments where theinjectable substance comprises a curable liquid, the cured material mayharden in the undercuts adjacent the stem portion 62, between the headportion 64 and the first rod end 32 c. The anchors 60 may provide a moresecure bond between the curable liquid and the first rod end 32 c.

The exemplary rod 10 c also has a cannulated second rod end 34 c with aduct 66 connecting the interior volume 138 with an injection port 68. Inthe embodiment shown, the injection port 68 is located at a side of therod end 34 c. In one embodiment, the injection port 68 is radiallydisposed. This is in contrast to the axially disposed port and valve 42shown in FIG. 3. Injectable materials may be introduced into the duct 66through the port 68 and ultimately flow into interior volume to expandthe expandable portion 30 c. In one embodiment, the rod 10 c comprises aself-sealing valve 70 that prevents the injectable substance fromescaping once the interior volume 38 is filled. In one embodiment, theself-sealing valve 70 is a check valve that is incorporated along theduct 66 to allow the injectable substance to flow towards the interiorvolume 38, but not out of the duct 66. In an alternative embodiment, theself-sealing valve 70 may be disposed at the injection port 68.

FIGS. 6A and 6B illustrate an alternative embodiment of a rod 10 d thatis characterized by a telescoping expandable portion 30 d. In contrastwith previous embodiments that use a flexible sheath or bellows design,the illustrated rod 10 d has a series of concentric columns 72 that areable to collapse within one another in the absence of an injectablematerial within the expandable portion 30 d. FIG. 6B illustrates thecollapsed rod 10 d. However, upon filling the expandable portion 30 dwith the injectable material, the concentric columns 72 expand ortelescope to the expanded position illustrated in FIG. 6A. In oneembodiment, the concentric columns 72 are substantially cylindrical. Inone embodiment, the concentric columns 72 have a substantiallynon-circular cross section, including for example, square, oval, star,or polygonal shapes. In one embodiment, the end portions 32, 34 maythemselves form concentric columns 72 with the expandable portion 30 dbeing a cavity formed in one or both of the end portions 32, 34. Theconcentric columns 72 may have seals (not shown) to prevent theinjectable substance from escaping once the expandable portion 30 d isfilled.

FIGS. 7A and 7B illustrate an exemplary rod 10 e having different rodends 32 e, 34 e than those provided on embodiments described above. Inthis particular embodiment, the rod ends 32 e and 34 e do not have anenlarged flange. Instead, the expanding portion 30 e is coupled directlyto clamping portions 33. Consequently, when the expandable portion 30 eis filled with an injectable substance as shown in FIG. 7B, the rod 10 ehas an outer width D that is substantially uniform over the entirelength of the rod 10 e. Also, the rod 10 e (or other rods 10 describedherein) may have an extended length L that is sufficient to span atleast one vertebral pair. Thus, the length L may be in the range betweenabout 30-40 mm or greater as needed. Rod 10 e may also have a cannulatedsecond rod end 34 e. Other means of introducing an injectable substancemay be incorporated into rod 10 e. This includes variations describedabove such as the radial insertion points in the rod end 32 e, 34 e orin the expandable portion 30 e.

FIGS. 8A and 8B illustrate an alternative configuration where rod 10 fincludes an expandable portion 30 f constructed of a non-compliant,flexible material 74. That is, the flexible material 74 is balloon-likein that it does not assume any particular shape when unfilled as shownin FIG. 8A. Further, the flexible material 74 of the expandable portion30 f is capable of expanding to a width that is larger than the width ofthe rod ends 32 f, 34 f as shown in FIG. 8B.

In embodiments discussed above, the exemplary rods 10 have generallycomprised an expandable portion 30 disposed between two rod ends 32, 34.In other embodiments, such as those illustrated in FIGS. 9 and 10, therods 10 g, 10 h are comprised of a plurality of expandable portions 30disposed in an alternating manner between clamping portions 33. Withthis multi-level configuration, the rods 10 g, 10 h may be attached toseveral vertebrae. In the embodiments shown, two expandable portions 30are arranged in an alternating manner between three clamping portions33. Accordingly, these embodiments may be attached at three points,possibly at three different vertebrae. Rods 10 comprising a largernumber of expandable portions 30 and clamping portions 33 are certainlyfeasible.

The embodiments illustrated in FIGS. 9 and 10 include multipleexpandable portions 30 with each portion 30 having substantially thesame size and construction. In some embodiments, the portions 30 havedifferent sizes. In some embodiments, each of the portions 30 is adifferent type.

The various rods 10 disclosed herein may be surgically implanted using avariety of techniques. Certainly, full-open surgical procedures that areused to install conventional rods may be used. However, thecompressibility of the expandable portion 30 of the rods 10 describedherein permits more minimally invasive surgical procedures. FIG. 11illustrates one such procedure where a mini-open procedure (i.e., with asmall surgical incision) is used. FIG. 11 shows a segment of a spinethat includes three vertebrae V1, V2, V3 and two discs D1, D2. In thisembodiment, the surgical procedure may be necessary to repair a diseasedor defective disc D1. Accordingly, a vertebral implant I may be insertedbetween vertebrae V1 and V2. Pedicle screws 14 similar to those shown inFIG. 1 are inserted into vertebrae V1 and V2 in preparation for theinstallation of a rod 10. Specifically, FIG. 11 shows rod 10 b from FIG.4 in a compressed and folded condition to pass through a small openingin the subject S. Rod 10 b is shown in FIGS. 11-13 for illustrativepurposes. In other embodiments, one or more of the other rod 10embodiments may be inserted using this surgical technique. The openingin the subject S may be widened as needed to allow the rod 10 b to pass.The widening may be accomplished using retractors R. Alternatively, theopening may be maintained between screw extenders that are coupled tothe installed pedicle screws 14. A dashed-line representation of aportion of exemplary screw extenders is shown in FIG. 11 and identifiedby the label SE.

The rod 10 b is placed into the subject S using an insertion tool, arepresentation of which is shown in dashed lines and labeled T. Then,the rod 10 b is positioned onto the pedicle screws 14 as shown in FIG.12. At this point, the rod 10 b, and particularly the expandable portion30 b remain in a compressed state. Once the rod 10 b is positioned asshown, a needle N or other injection instrument is used to inject theinjectable substance into the self-sealing valve 58 on the expandableportion 30 b. Note that with other embodiments, the injectable substancemay be injected into other portions of the rod 10 such as radially oraxially into the rod end 34.

As the injectable substance is placed into the expandable portion 30 b,the rod ends 32, 34 separate from each other until the enlarged flanges35 at each rod end 32, 34 contact the head of the pedicle screws 14. Theexpanded rod 10 b is illustrated in FIG. 13. At this point, the rod 10 bis fully seated and a suitable clamping device (e.g., retaining cap 16shown in FIG. 1) can be used to secure the clamping portion 33 to thepedicle screws 14. In an alternative approach, the clamping portions 33may be secured to the pedicle screws 14 prior to the insertion of someor all of the substance. For example, inserting additional substanceinto the rod 10 b after the clamping portions 33 are secured to thepedicle screws 14 may provide some desired distraction of the vertebraeto which the pedicle screws 14 are attached.

An alternative installation approach contemplates a minimally invasivepercutaneous procedure as shown in FIGS. 14 and 15. The procedure shownin FIG. 14 incorporates an installation instrument 20. One example of aninstrument suitable for this type of installation is the Sextant RodInsertion System available from Medtronic Sofamor Danek in Memphis,Tenn., USA.

The installation instrument includes support arms 78 that are coupled topedicle screw extensions 76. The support arms 78 are pivotally connectedto a rod holder 82 about pivot P. As with the previous method shown inFIGS. 11-13, this procedure may include removing some or all of anintervertebral disc D1 from the space between first V1 and second V2vertebral bodies through one percutaneous puncture in the subject. Animplant I is introduced into the disc space. Implant I may be aninterbody fusion device or the like as is known in the art. The firstand second pedicle screws 14 and pedicle screw extensions 76 are engagedto the first and second vertebrae V1, V2, respectively, through secondand third percutaneous punctures in the subject S. If desired, a surgeoncan manipulate the pedicle screw extensions 76 to apply a load tocompress or distract the vertebrae V1, V2 prior to installing rod 10 e.Rod 10 e is shown for illustrative purposes. Any of the other rod 10embodiments may be inserted using this technique. The rod 10 e isinstalled through a fourth percutaneous puncture in the subject S usingthe installation instrument 20. The rod 10 e is brought into engagementwith the pedicle screws 14 by rotating the rod holder 82 about pivot P.

In one embodiment, the rod holder 82 is cannulated to allow a surgeon tointroduce an injectable substance through the rod holder 82 and into therod 10 e. A needle or other injection instrument is used to inject theinjectable substance into the port J in the rod holder 82. As theinjectable substance is inserted into the expandable portion 30 e, therod ends 32, 34 separate from each other until the clamping portions 33at each rod end 32, 34 lie within the head of the pedicle screws 14.This is illustrated in FIG. 15. At this point, the rod 10 e is fullyseated and a suitable clamping device (e.g., retaining cap 16 shown inFIG. 1) can be used to secure the clamping portion 33 to the pediclescrews 14.

Since the rod 10 includes clamping surfaces 33 on either side of anexpandable portion 30, a surgeon may clamp down on the rod ends 32, 34regardless of the phase of the injectable material. That is, regardlessof whether the injectable substance is gaseous, liquid, or an uncuredliquid, the surgeon may secure the rod 10 to the pedicle screws 14 orother clamping mechanism once the rod ends 32, 34 have expanded to thedesired position. This aspect also means a surgeon may be able to securethe rod ends 32, 34 without having to wait for a curable injectablesubstance to set.

Spatially relative terms such as “under”, “below”, “lower”, “over”,“upper”, and the like, are used for ease of description to explain thepositioning of one element relative to a second element. These terms areintended to encompass different orientations of the device in additionto different orientations than those depicted in the figures. Further,terms such as “first”, “second”, and the like, are also used to describevarious elements, regions, sections, etc and are also not intended to belimiting. Like terms refer to like elements throughout the description.

As used herein, the terms “having”, “containing”, “including”,“comprising” and the like are open ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a”, “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

The present invention may be carried out in other specific ways thanthose herein set forth without departing from the scope and essentialcharacteristics of the invention. For example, embodiments describedabove have contemplated end members 32, 34 that have a substantiallysimilar overall shape. However, this is not explicitly required. Forinstance, other embodiments may include an end member at one end or anintermediate location having a flange while end members in otherlocations do not have a flange. The present embodiments are, therefore,to be considered in all respects as illustrative and not restrictive,and all changes coming within the meaning and equivalency range of theappended claims are intended to be embraced therein.

1-49. (canceled)
 50. A spinal rod system comprising: first and secondanchors having a transverse member for receiving a first end member anda second end member, the first end member having an axial end portionseated into the first anchor such that the first end member is preventedfrom moving beyond the first anchor; the second end member having anaxial end portion seated into the second anchor such that the second endmember is prevented from moving beyond the second anchor; and anintermediate section connected to the first and second end members; anda port operatively connected to the intermediate section; theintermediate section being axially expandable upon the introduction of asubstance into the port, the intermediate section being rigid before theintroduction of the substance into the port, the intermediate sectionbeing expandable between a first size to space the first and second endmembers a first distance apart and a second enlarged size to space thefirst and second end members a second greater distance apart.
 51. Thespinal rod system of claim 50, wherein the intermediate section isconfigured to apply a distraction force to vertebral members after theaxial end portion of the first end member is fixed into the first anchorand the axial end portion of the second end member is fixed into thesecond anchor upon introduction of the substance into the port.
 52. Thespinal rod system of claim 50, wherein the first end member engages thefirst anchor and the second end member engages the second anchor suchthat the first and second anchors are disposed to penetrate bone in atransverse orientation in relation to the first and second end members.53. The spinal rod system of claim 50, wherein the intermediate sectionis rigid after the introduction of the substance into the port.
 54. Thespinal rod system of claim 50, wherein the intermediate section isflexible after the introduction of the substance into the port.
 55. Thespinal rod system of claim 50, wherein the port is axially disposed inone of the end members.
 56. The spinal rod of claim 50, wherein the portis radially disposed in one of the end members.
 57. The spinal rod ofclaim 50, wherein the port is disposed in the intermediate section. 58.The spinal rod of claim 50 wherein each of the first and second endmembers have a width that is substantially equal to that of theintermediate section when the intermediate section is expanded to thesecond enlarged size.
 59. The spinal rod of claim 50 wherein theintermediate section comprises multiple concentric columns having widthsthat permit the columns to collapse within one another when theintermediate section is at the first size, the concentric columnsextending axially relative to one another when the intermediate sectionis expanded to the second enlarged size.
 60. The spinal rod of claim 50further comprising a third member and a second intermediate section, thethird member having a clamping portion to be operatively connected witha vertebral member, and the third member positioned between theintermediate section and the second intermediate section.
 61. The spinalrod of claim 50 wherein the intermediate section is a chamber disposedin at least one of the two end members.
 62. The spinal rod of claim 50wherein the first end member has a perforated protrusion extendinginwardly.
 63. The spinal rod of claim 62 wherein the second end memberhas a perforated protrusion extending inwardly.
 64. A spinal rod systemcomprising: first and second anchors having a transverse member forreceiving a first end member and a second end member, the first endmember having an axial end portion seated into the first anchor suchthat the first end member is prevented from moving beyond the firstanchor, the first end member having a perforated protrusion extendinginward; the second end member having an axial end portion seated intothe second anchor such that the second end member is prevented frommoving beyond the second anchor, the second end member having aperforated protrusion extending inward; and an intermediate sectionconnected to the first and second end members; and a port operativelyconnected to the intermediate section; the intermediate section beingaxially expandable upon the introduction of a substance into the port,the intermediate section being rigid before the introduction of thesubstance into the port, the intermediate section being expandablebetween a first size to space the first and second end members a firstdistance apart and a second enlarged size to space the first and secondend members a second greater distance apart, wherein the intermediatesection is configured to apply a distraction force to vertebral membersafter the axial end portion of the first end member is fixed into thefirst anchor and the axial end portion of the second end member is fixedinto the second anchor upon introduction of the substance into the port,wherein the first end member engages the first anchor and the second endmember engages the second anchor such that the first and second anchorsare disposed to penetrate bone in a transverse orientation in relationto the first and second end members.
 65. A spinal rod system comprising:first and second anchors having transverse members for receiving a firstcoupling member and a second coupling member, the first coupling memberhaving an axial end portion seated into the first anchor such that thefirst coupling member is prevented from moving beyond the first anchor;the second coupling member having an axial end portion seated into thesecond anchor such that the second coupling member is prevented frommoving beyond the second anchor; an axial member operatively connectedto and extending between the first and second coupling members; aninterior section formed by the axial member, the interior section beingconstructed to contain a substance introduced into the interior section,the axial member constructed to become elongated upon introduction ofthe substance into the interior section; and a port operativelyconnected with the interior section for introducing the substance, theport being disposed in the axial member, wherein the axial member isconfigured to apply a distraction force to vertebral members after theaxial end portion of the first coupling member is fixed into the firstanchor and the axial end portion of the second coupling member is fixedinto the second anchor, wherein the first coupling member engages thefirst anchor and the second coupling member engages the second anchorsuch that the first and second anchors are disposed to penetrate bone ina transverse orientation in relation to the first and second couplingmembers.
 66. The spinal rod of claim 65 wherein the first couplingmember comprises an anchor feature extending into the interior sectionfrom the first surface.
 67. The spinal rod of claim 66 wherein theanchor feature comprises a perforated protrusion.
 68. The spinal rod ofclaim 66 wherein the anchor feature comprises an enlarged head portion.69. The spinal rod of claim 65 further comprising a third couplingmember and a second axial member, the third having a clamping portion tobe operatively connected with a vertebral member, and the third memberpositioned between the intermediate section and the second intermediatesection.